in reply to
no server response required
(I am taking for granted that the OP is addressing a Perl-based CGI or FastCGI handler ... therefore, that the question is being asked in an appropriate venue.)
my understanding that requests issued, at least to Apache, must be replied-to. You might be able to use a different HTTP server, but actually, I think this is a requirement of the HTTP protocol.
(I'd be a little surprised if your browser didn’t get upset about it, too ...)
Can you perhaps return 204 No Content? (See: this WikiPedia page...) Now, you are fulfilling the handshake obligation of the protocol, but saying that there is nothing else to say.